Chop leeks into small pieces and saute in water in a pan until soft. In a food processor put potato flakes, soy milk, and leeks and blend until fairly smooth and leek pieces are pretty chopped up. Pour mixture into a sauce/soup pan and add 2 cups water (or more soy milk if you want creamy). Stir and heat through on medium-medium/high heat until heated through. Season as desired.

I used a salt-free garlic seasoning, but some may find it too bland and might want to add some salt.